In recent years, a vehicle such as an automobile has a radar apparatus which, based on a radiated electromagnetic wave and a received wave reflected, measures, for example, a relative distance to an object such as another vehicle, a pedestrian, and an object placed on a road, which is present around the own vehicle, a relative velocity of the object, and the direction (azimuth) in which the object is present. The own vehicle having such a radar apparatus further has, for example, an apparatus which, based on the relative distance, the relative velocity, and the azimuth measured by the radar apparatus of the own vehicle, makes control for running while automatically maintaining the distance between the own vehicle and the object, in order to reduce a burden on a driver upon driving, or to enhance safety of a passenger.
The radar apparatus of the own vehicle generates data indicating, as measured information, the relative distance, the relative velocity, and the azimuth of the object, every time a predetermined time interval passes. However, the measured information generated by the radar apparatus has dispersion, error, or the like. Therefore, it is necessary to convert the measured information into smoothed information indicating smoothly the movement of the object by performing filtering processing on the measured information. One example of radar apparatuses performing such processing is a millimeter-wave radar apparatus (hereinafter, referred to as conventional technique) disclosed in Patent Document 1.
The degrees of dispersion of the measured information are different in a radiation area of an electromagnetic wave because the S/N ratios of the measured information are not uniform in the radiation area. In consideration of this, in the conventional technique, a gain of a filter for the filter processing is changed in accordance with the position of an object in the radiation area. For example, in the conventional technique, a gain of the filter is set relatively small in a portion of the radiation area in the middle thereof and near the radar apparatus because the degrees of dispersion of the measured information are relatively small in the portion, the radiation area radially spreading from the radar apparatus. The gain of the filter is set relatively large in a portion of the measurement area in the middle thereof and far from the radar apparatus because the degrees of dispersion of the measured information are relatively large in the portion. The gain of the filter is set largest in the other portion because the degrees of dispersion of the measured information are largest in the other portion. Thus, in the conventional technique, the gain of the filter is changed in consideration of the degrees of dispersion of the measured information which are different depending on the position of the object in the radiation area, whereby the accuracy of the smoothed information is prevented from being changed.    PATENT LITERATURE 1: Japanese Laid-Open Patent Publication No. 2001-242242